How can I loop through a json result by substituting field/column names with a variable

Question

How can I loop through a json result by substituting column names for a variable

End result: I'm building a table from a list (~25 columns). I want to attach custom classes to each cell based on the cell's value during the loop to parse json data.

I made a REST call for list items in one function, and am looping through the results in another.

1. I'm using the for loop for(i=0; i<data.d.results.length; i++)
2. I'm building the table within the loop

$displayTable = $displayTable + $cellClass + $eventClass + data.d.results[i].columnName_1 + $cellClose;

$displayTable = $displayTable + $cellClass + $eventClass + data.d.results[i].columnName_2 + $cellClose;

3. I want to attach an additional class to all instances based on their values using an if, statement.

4. Is there a way to loop through the json result by substituting column names for a variable? It'll make it easier both to write comparison statements with each value on the list and make it easier to display (loop) all columns without writing out 25 column names.

An example will be using a $cellInstance variable variable instead of a column/field name as seen in point 2 above. This would be able to

``$displayTable = $displayTable + $cellClass + $eventClass + data.d.results[i].$cellInstance + $cellClose;`

Answer 1

I can think of a couple of Options:

1: Get all fields in item from rest and filter out SharePoint Default fields.

2: create a new Content type which contains all desired fields.

_api/web/lists/getbytitle('Samples')/contenttypes
_api/web/lists/getbytitle('Samples')/contenttypes('"+ contentType +"')/fields

first one gets all Content types. Note there are trash one in the one you want to filter out of the results with ?filter=

Second one gets all field in the specific contenttype

And please use the following in your for loop:

var length = data.d.results.length;
for(var i = 0; i < length; i++) {
// your code
}

Why this is better:

1: lets say you have 100 items your Loop is checking if data.d.results.length is a valid int.

2: i = 0; makes a global variable. If you have this asyn this or something else that runs asyn and reuse 1 you can get confusing results. Also changing global variables is slower.

Hope this helps.

If you have questions, I won't be able to respond before monday.

Answer 2

Somehow this question got bumped up (by the Community bot?), and even though it's years out of date and I don't expect the OP to be around to accept it as an answer, I still can't help but leave an answer here in case someone stumbles on this in the future.

You can access JSON property values by using dot notation, which is what you usually see (and the OP shows an example of):

data.d.results[i].columnName_1

However, you can also access JSON property values using bracket notation, which looks similar to indexing into an array, but you use a string of the property name:

data.d.results[i]["columnName_1"]

Because you can use strings like that in bracket notation, you can instead use a variable there, and change the value of the variable to whichever property you want to get the value of.

So in the OP's case, you could do something like

var columNames = ["column_1", "column_2", "column_3", "column_4"];

for (var i = 0; i < data.d.results.length; i++) {
    
    // get the current item
    var item = data.d.results[i];

    // loop through the column names
    for (var j = 0; j < columnNames.length; j++) {

        // get the current column
        var currentColumn = columnNames[j];

        // get that column's value using bracket notation
        $displayTable += $cellClass + $eventClass + item[currentColumn] + $cellClose;
    }
}